Spatial Relationships between Canopy Structure and Understory Vegetation of an Old-Growth Douglas-Fir Forest

Leaf area index (LAI) in old-growth Douglas-fir (Pseudotsuga menziesii var menziesii (Mirb.) Franco) forests exceeds that of any other forest ecosystem by some estimates; however, LAI determinations in coniferous forests have generally been indirect, involving extrapolations of patterns observed in younger stands. Aided by a 75-m construction crane for canopy access, we used a vertical line-intercept method to estimate LAI for a [Formula: see text]450-year-old Douglas-fir - western hemlock (Tsuga heterophylla (Raf.) Sarg.) forest in southwestern Washington state. LAI was calculated as the product of foliage contact frequency and an "extinction coefficient" accounting for foliage angular distribution, geometry, and the ratio of "interceptable" to total leaf area. LAI estimates were 9.3 ± 2.1 (estimate ± 95% confidence interval), 8.5 ± 2.2, and 8.2 ± 1.8 in 1997, 1998, and 1999, respectively, or 8.6 ± 1.1 pooled across years. Understory vegetation, including foliage of woody stems <5 cm diameter, represented 20% of this total. Sample points in which Douglas-fir was dominant had a higher total LAI than points dominated by western hemlock, including a higher LAI of understory vegetation. Our results do not support the contention that old-growth Douglas-fir - western hemlock forests maintain an appreciably higher LAI than do other forest ecosystems. Moreover, LAI in very old stands may decline as western hemlock replaces Douglas-fir through the course of succession.

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Canopy gaps in Douglas-fir forests of the Cascade Mountains

Canadian Journal of Forest Research ◽

10.1139/x90-087 ◽

1990 ◽

Vol 20 (5) ◽

pp. 649-658 ◽

Cited By ~ 144

Author(s):

Thomas A. Spies ◽

Jerry F. Franklin ◽

Mark Klopsch

Keyword(s):

Canopy Structure ◽

Douglas Fir ◽

Western Hemlock ◽

Permanent Plots ◽

Gap Size ◽

Gap Formation ◽

Seedling Density ◽

Old Growth ◽

Mature Stand ◽

Mature Stands

Types and rates of mortality were measured and canopy gap formation rates were estimated from 5- to 15-year records of mortality in 34 permanent plots in mature (100- to 150-year-old) and old-growth (>200-year-old) Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco)/western hemlock (Tsugacanadensis (Raf.) Sarg.) forests in western Oregon and Washington. Gap surveys were conducted in a mature and an old-growth stand, and characteristics of 40 gaps and regeneration were measured. Most canopy trees died without disrupting the forest in both mature (87.6%) and old-growth stands (73.3%). The amount of forest area per year representing new gaps was 0.7% in mature stands and 0.2% in old-growth stands. The gap survey found a higher proportion of gaps in the mature stand than in the old-growth stand. Most regeneration (> 1 m tall) in gaps was western hemlock; Douglas-fir regeneration did not occur. The ratio of seedling density in gaps to density under canopies was about 3 for the mature stand and about 9 for the old-growth stand. Seedling density was correlated with measures of gap age but not gap size. The study suggests that gap disturbances and vegetative responses are important processes in the dynamics of these forests. However, gap formation rates and vegetative responses appear to be slow relative to other forest types. In addition to gap size, canopy structure and disturbance severity are important determinants of gap response.

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Inventory and value of old-growth in the Douglas-fir region.

10.2737/pnw-rn-437 ◽

1986 ◽

Cited By ~ 4

Author(s):

Richard W. Haynes

Keyword(s):

Douglas Fir ◽

Old Growth

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Comparison of Methods of Estimating Leaf-Area Index In Old-Growth Douglas-Fir

Ecology ◽

10.2307/1939820 ◽

1986 ◽

Vol 67 (4) ◽

pp. 975-979 ◽

Cited By ~ 106

Author(s):

J. D. Marshall ◽

R. H. Waring

Keyword(s):

Leaf Area Index ◽

Leaf Area ◽

Douglas Fir ◽

Comparison Of Methods ◽

Old Growth ◽

Area Index

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Canopy disturbances over the five-century lifetime of an old-growth Douglas-fir stand in the Pacific Northwest

Canadian Journal of Forest Research ◽

10.1139/x02-030 ◽

2002 ◽

Vol 32 (6) ◽

pp. 1057-1070 ◽

Cited By ~ 29

Author(s):

Linda E Winter ◽

Linda B Brubaker ◽

Jerry F Franklin ◽

Eric A Miller ◽

Donald Q DeWitt

Keyword(s):

Pacific Northwest ◽

Variable Density ◽

Tsuga Heterophylla ◽

Douglas Fir ◽

Western Hemlock ◽

Old Growth ◽

The Pacific ◽

History Of ◽

Horizontal Heterogeneity ◽

Restoration Strategies

The history of canopy disturbances over the lifetime of an old-growth Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) stand in the western Cascade Range of southern Washington was reconstructed using tree-ring records of cross-dated samples from a 3.3-ha mapped plot. The reconstruction detected pulses in which many western hemlock (Tsuga heterophylla (Raf.) Sarg.) synchronously experienced abrupt and sustained increases in ringwidth, i.e., "growth-increases", and focused on medium-sized or larger ([Formula: see text]0.8 ha) events. The results show that the stand experienced at least three canopy disturbances that each thinned, but did not clear, the canopy over areas [Formula: see text]0.8 ha, occurring approximately in the late 1500s, the 1760s, and the 1930s. None of these promoted regeneration of the shade-intolerant Douglas-fir, all of which established 15001521. The disturbances may have promoted regeneration of western hemlock, but their strongest effect on tree dynamics was to elicit western hemlock growth-increases. Canopy disturbances are known to create patchiness, or horizontal heterogeneity, an important characteristic of old-growth forests. This reconstructed history provides one model for restoration strategies to create horizontal heterogeneity in young Douglas-fir stands, for example, by suggesting sizes of areas to thin in variable-density thinnings.

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